Light loading on 2nd pole of filter

Discussion in 'General Electronics Chat' started by lasteem1, May 5, 2011.

  1. lasteem1

    Thread Starter New Member

    Apr 10, 2009
    1
    0
    So my boss is explaining a 2 pole filter to me and for the most part it is straight forward. However he mentions that the 2nd pole of the filter is "lighter load so it doesn't affect the corner frequency". In his schematic the C is smaller and the R is larger on the 2nd pole. Can anyone give me any clarification as to why exactly this is necessary. I've attached a pic of the schematic.[​IMG]
     
  2. #12

    Expert

    Nov 30, 2010
    16,330
    6,818
    I think the instructor told you why it is necessary.

    For further clarification, imaging a perfect buffer amplifier (infinite input impedance, gain of 1) between the two filter sections and do the math to find the "ideal" response. Then change C9 and R24 to match the values of C8 and R23, leave out the imaginary perfect buffer amp, and do the math again, bearing in mind that C9 and R24 impose a load on the first section.

    This is an excellent exercise for your education.
     
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